How can I read a file into bytes, and find a string of hex to match?

debugcn Published at Dev

DropItLikeItsHot

I want to read a file's content and find hex matches in the data. I feel like using "file.readallbytes" is overkill because I just need to read byte by byte until I find a hex match. Is there a better alternative I can use instead or is better for performance to use readallbytes? What I'm doing below currently works as is.

The file I am attempting to read is a simple text file, it has "hello" in it.

string match = "68656C6C6F";

foreach (var jsfile in jsscan)
{
    byte[] data = File.ReadAllBytes(jsfile);
    string dataString = String.Concat(data.Select(b => b.ToString("X2")));
    if (dataString.Contains (match))
    {
        MessageBox.Show(jsfile + dataString);
    }
}

Updated solution thanks to mfatih:

public void example()
{

    string match = "68656C6C6F"; //This is "hello" in hex
    byte[] matchBytes = StringToByteArray(match);


    foreach (var jsFile in jsscan)
    {
        using (var fs = new FileStream(jsFile, FileMode.Open))
        {
            int i = 0;
            int readByte;
            while ((readByte = fs.ReadByte()) != -1)
            {
                if (matchBytes[i] == readByte)
                {
                    i++;
                }
                else
                {
                    i = 0;
                }
                if (i == matchBytes.Length)
                {
                    Console.WriteLine("It found between {0} and {1}.", 
                       fs.Position - matchBytes.Length, fs.Position);
                    break;
                }
            }
       }
    }
}
public static byte[] StringToByteArray(String hex)
{
    int NumberChars = hex.Length;
    byte[] bytes = new byte[NumberChars / 2];
    for (int i = 0; i < NumberChars; i += 2)
            bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
    return bytes;
 }

mfatih

There's a more efficient way without reading into the whole file. I hope this way can help you.

string match = "68656C6C6F";

byte[] matchBytes = Encoding.ASCII.GetBytes(match);

foreach (var jsFile in jsscan)
{
    using (var fs = new FileStream(jsFile, FileMode.Open))
    {
        int i = 0;
        int readByte;
        while ((readByte = fs.ReadByte()) != -1)
        {
            if (matchBytes[i] == readByte)
            {
                i++;
            }
            else
            {
                i = 0;
            }
            if (i == matchBytes.Length)
            {
                Console.WriteLine("It found between {0} and {1}.", 
                       fs.Position - matchBytes.Length, fs.Position);
                break;
            }
        }
   }
}

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